Golfers have a constant desire to hit long and accurate shots. In developing higher performance golf balls or golf clubs to meet this desire, it is very important to analyze the contact phenomenon between a golf ball and a golf club.
However, the following factors cause difficulty in analyzing what kind of phenomenon occurs on the contact surface between the golf ball and the golf club.
(1) The duration of the contact phenomenon between the golf ball and the golf club is short (about 0.5 msec).
(2) Since the contact phenomenon is significantly influenced by the contact surface with the golf club, it is desirable to recognize the state of the contact surface, but the contact surface is hidden and is unobservable.
The factor (1) can be solved by using a high-speed camera or the like.
The factor (2), however, remains unsolved, and there is the need to develop a technique that can solve the problem. Forces acting on the ball include the contact force from the club. The contact force can be divided into a normal direction component and a friction force component. In particular, the friction force changes significantly due to, for example, small slippage of the contact surface. Conventional study has revealed that the spin of the ball changes when the club surface (material, grooves, surface roughness, etc.) is changed, which may significantly affect the carry in the case of drivers and the force of stopping (accuracy) after landing in the case of irons.
As a technique for predicting the amount of spin of a golf ball, for example, Patent Literature (PTL) 1 discloses the following method of measuring the coefficient of kinetic friction of a golf ball and an impact plate tilted at a predetermined angle with respect to the flight direction of the golf ball when the golf ball impacts the impact plate: The time function of the contact force in the direction perpendicular to the impact plate and the time function of the contact force in the direction parallel to the impact plate are simultaneously determined, and the coefficient of kinetic friction is calculated based on a specific relational expression.